1,721,017 research outputs found
Nitrogen and phosphorous budgets during a farming cycle of the Manila clam Ruditapes philippinarum: An in situ experiment
No full textMicrophytobenthos activity and fluxes at the sediment-water interface: interactions and spatial variability
No full textDenitrification and benthic metabolism in lowland pit lakes: The role of trophic conditions
No full textOver recent decades, a great number of pit lakes have been formed, as a result of sand and gravel quarrying in river floodplains that are often also heavily exploited for agriculture. These lakes can act as nutrient filters and regulate the nitrogen pollution resulting from agricultural fertiliser use. In this paper we report the main outcomes of a study of the major nitrogen pathways in five pit lakes of differing trophic status, located along a lowland stretch of the Po river (Northern Italy). Benthic nitrogen fluxes and denitrification rates were determined in the hypolimnion and denitrification and reactive nitrogen assimilation by microphytobenthos in the littoral zone. We tested the hypothesis that lake depth and trophic status can impair denitrification and/or reactive nitrogen assimilation, compromising the function of the lakes as nutrient filters. In the studied lakes, denitrification and reactive nitrogen assimilation by primary producer communities accounted for substantial nitrogen removal rates, which were among the highest reported in the literature. Benthic nitrogen fluxes and denitrification varied between and within lakes, with depth. The littoral zone and surface waters also supported primary production, favouring nitrogen assimilation and temporal retention in the primary producer biomass. In all lakes, denitrification rates decreased from littoral to hypolimnetic sites. Denitrification rates and net nitrogen assimilation also diminished from oligotrophic to eutrophic conditions. To some extent, in eutrophic lakes there was a transfer of primary production from the benthos to the water column and the benthic system became heterotrophic, reducing the capacity for net nitrogen removal. Overall these results highlight that floodplain pit lakes can provide ecosystem services formerly supplied by natural wetlands. An important factor for management is the development of extensive littoral and shallow water zones, which are critical for maximising the nitrogen removal
Monitoring phosphorus in the tributaries of a deep lake from the perspective of the receiving water body
Full text linkDeep lakes under climate change are experiencing reduced deep mixing, with a consequent increase in nutrients concentration and oxygen deficit in the hypolimnion. From this perspective, greater efforts should be made to reduce the phosphorus load delivered to these lakes by their tributaries. An essential precondition for this action is a reliable estimate of the loads, which is challenging due to the marked temporal variability of the hydrologically-driven diffuse sources. In this article, we used a high-resolution phosphorus time series measured at the mouth of the main tributary of Lake Iseo and a machine learning algorithm to show the dominant role played by the acute, storm-dependent transport. The results emphasize the need to control loads strictly linked to precipitation and runoff in the drained watershed, representing 31% of the observed events but responsible for 64% of the overall load to the lake. We also proved evidence that the current obligations on nutrients monitoring miss the total phosphorus dynamics, leading to a systematic underestimation of the load conveyed by the inflows. Accordingly, we propose a sampling methodology where the timing and the methods for data interpolation are established according to the hydrological conditions in the drained watershed. Accounting for the economical and practical constraints imposed by the monitoring authorities, we propose to integrate, at the mouth of lake tributaries, a monthly manual sampling with an auto-sampler programmed to fill 2 bottles in correspondence of each high flow event. Our simulations showed that in this case the load estimation error was reduced below 1%, implying, on average, 13 field surveys/year and 21 laboratory analyses/year only. It is reasonable to expect comparable performances in hydrologically similar watersheds
Benthic primary production and bacterial denitrification in a Mediterranean eutrophic coastal lagoon
No full textMicrophytobenthos and macroalgal mats are simultaneously present in eutrophic lagoons and are expected to have different direct and indirect effects on nitrogen related processes through uptake and inhibition or stimulation of microbial activity. To assess the relative contribution of different primary producer communities and heterotrophic processes to benthic nitrogen cycling, we studied nitrogen uptake and bacterial denitrification in the eutrophic Sacca di Goro lagoon (northern Italy). Benthic fluxes of oxygen and dissolved inorganic nitrogen (DIN), and rates of nitrification-coupled (Dn) and water-nitrate (Dw) denitrification were measured every 30-45. days for one year at two shallow sites. Station Giralda is close to the main freshwater inlet, has turbid waters and muddy-organic and bioturbated sediments with microphytobenthos (MPB). Station Gorino is brackish with muddy-sand sediments which are covered by macroalgal mats of the genus Ulva. Here, sediment patches with and without macroalgae (MA) were simultaneously studied.Sediments with MPB were net heterotrophic and regenerated large amounts of ammonium to the water column. At Gorino, sediments with MA were net autotrophic through the year, and DIN fluxes were mainly controlled by macroalgal uptake. On an annual basis, denitrification rates were three fold higher at Giralda (2.27±0.06molNm-2yr-1) than at Gorino (0.83±0.01molNm-2yr-1), due to higher nitrate in the water column and nitrification in surface sediments. At Gorino, denitrification was one order of magnitude lower than DIN uptake by macroalgae (10.39±1.30molNm-2yr-1). Nevertheless, the differences between denitrification rates in sediments with and without MA were unexpectedly negligible, showing that the denitrification capacity was not suppressed by macroalgal competition. Results from this study suggest that in eutrophic lagoons nitrogen cycling seems less affected by MPB compared to more oligotrophic coastal waters and that most of the available DIN flows through benthic macroalgae. However, Ulva is only a temporary N-sink and most of its nitrogen pool can be either rapidly recycled or exported by tidal currents to the open sea. © 2012 Elsevier B.V
Short-term influence of recolonisation by the polychaete worm Nereis succinea on oxygen and nitrogen fluxes and denitrification: a microcosm simulation
No full textImpact of a trout farm on the water quality of an Apennine creek from daily budgets of nutrients.
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Assessing the potential impact of clam rearing in dystrophic lagoons: an integrated oxygen balance
No full textIn this work we propose an integrated model to simulate the oxygen balance of a eutrophic lagoon exploited for mollusks farming. The balance is determined by macroalgal primary production and respiration rates plus the oxygen demand by clams and sediment. The aim is to evaluate the impact of intensive clam rearing on the vulnerability of the lagoon ecosystem to anoxic crises. The model is based on field data collected in the Sacca di Goro lagoon (Po River Delta) and has a stochastic formulation accounting for environmental unpredictability. The results show that clams have a considerable impact on the ecosystem, i.e. densities of 500 clams m-2 can cause hypoxic events (DO < 2 mgO2 L-1) in June and September, whilst densities over 1000 clams m-2 (one half the maximum observed seeding densities) can determine a state of chronic hypoxia during the whole summer period, with minimum DO values lower than 1 mgO2 L-1. The model provides a valuable tool for assessing the sustainability of different rearing policies
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